1. Field of the Invention
This invention relates to the field to the field of timers capable of generating multiple series of timing pulses produced in interleaved groups consisting of a certain number of pulses of one series followed by a certain number of pulses of a second series. All of the pulses are used to generate timing signals by which different but related actions of one or more persons using the apparatus can be timed. In particular the invention relates to the field of cardiopulmonary resuscitation (CPR) and, to means for timing the actions of one or two rescuers working to revive a victim of any age from infancy to adulthood.
2. The Prior Art
CPR is the technique of reviving a victim whose heart and lung actions have just stopped, or at least of maintaining flow of oxygenated blood in the victin's cardiovascular system by non-surgical techniques to prevent inreversible brain damage until the victim can be taken to a properly equipped medical facility or until a doctor determines that further efforts are useless.
There are two different but related activities that must be carried out in CPR. One is to apply pressure in impulses, or compressions, to the victim's chest to produce a pumping action that achieves an effect somewhat similar to normal heart operation. The circulation produced by such externally applied pumping depends on the amount of pressure (which must not be excessive) on the victim's chest at each compression and on the number of compressions per minute.
The other activity is to force oxygen into the victim's lungs. This is accomplished by periodically closing the victim's nose and somewhat forcefully exhaling air through the rescuer's mouth directly into the victin's mouth in a prescribed manner. This is called ventilation. While the air thus blown into the victim's lungs includes some carbon dioxide from the rescuer's own lungs, it also includes sufficient oxygen to supply at least the amount necessary to prevent damage to the victim's brain.
There is some difference of opinion as to the exact number of compressions and ventilations per sequence of the two activities and the exact rate at which each should be performed in each sequence, but it is uniformly agreed that infants and small children require more compressions per minute than do adults. Currently, the best opinion is that there should be three different chest compression rates, depending on whether the victim is an adult, a child, or an infant.
If there are two or more rescuers, one can apply compressions at a steady rate sufficient to induce adequate systolic blood pressure in the victim and therefore adequate flow. The other rescuer can apply ventilations without interfering with the compressions. The timing is relatively simple, merely requiring signals at one repetition rate to guide the person applying compressions and detectably different signals at another rate to guide the person giving the lung ventilations.
However, if there is only a single rescuer, it takes a short length of time for the rescuer to move from the proper position for applying chest compressions to an adult or child victim to the position for applying ventilation to such a person. This necessitates applying compressions at a faster rate to achieve a higher systolic blood pressure than in the two rescuer cases so that, when the compressions are momentarily stopped in order to apply ventilation, the blood pressure will not diminish to too low a level.
In the case of an infant, even a single rescuer does not have to change position to go from applying compression to applying ventilation and therefore the compressions need not be interrupted but can continue at a uniform, fairly high rate even while the infant's lungs are being ventilated at a relatively low rate.
Typical rates for compressions are:
______________________________________ adult victim, two rescuers 60/minute adult victim, one rescuer 80/minute child victim, two rescuers 80/minute child victim, one rescuer 100/minute infant victim, one resucer 120/minute ______________________________________
One lung ventilation is given synchronously with each fifth compression if there are two rescuers or if the victim is an infant. The sequence for a single rescuer of an adult or child is fifteen compressions at the appropriate rate followed by two ventilations rhythmically given within five seconds. It is easy to forget the correct numbers and even easier to lose count, especially in the case of a single rescuer. it is also easy to apply the compressions unevenly unless automatic timing means are used.